1. Field of the Invention
The present invention relates to a cooling structure of a projection tube incorporated in a projection TV set, for example.
2. Description of the Related Art
Recently, projection TV sets having a large screen of not less than 40 inches have been popularly used. The projection TV set is served for projecting an image of a projection tube (PRT) having a screen size of approximately 5.5 inches on a screen of approximately 40 inches using an optical lens, a mirror and the like. In general, a color image is obtained by projecting images from three projection tubes which respectively produce monochroic images of red, green and blue on a screen. In the projection system, for example, to project the image of approximately 5.5 inches of the PRT on the screen of 40 inches, the image is magnified by not less than 50 times in area. Accordingly, the image of the PRT is required to have an extremely high brightness. To realize the high brightness, it is necessary to supply a large current to the small screen of approximately 5.5 inches and this elevates the temperature of a phosphor screen and a panel glass. The elevation of the temperature of the phosphor screen gives rise to a problem such as the lowering of light emitting efficiency of a phosphor body or the breaking of the panel glass due to the thermal distortion.
To solve this problem, it is necessary to cool the phosphor screen. U.S. Pat. No. 4,731,557 discloses one typical cooling structure. In this cooling structure, to seal a coolant in a chamber, seal members are provided at two locations and the chamber is sealed by a mechanical pressure exerted by these seal members. However, this cooling structure still has several drawbacks including following drawbacks. That is, when a defect exists in the seal member at one location, the liquid leaks from the chamber. Further, since it is necessary to mechanically fasten the seal members using bolts or the like to respectively seal at two locations, the manufacturing cost is pushed up.